Mass is a measure of the amount of matter in an objector subject. Monoisotopic mass and the average mass are two mass measurements common in the field of chemistry. Both are based on the masses of isotopes.
What is the difference between monoisotopic mass and average mass? Monoisotopic mass is the mass of a molecule calculated using the mass of the most abundant isotope of each element present, whereas average mass is the weighted average of the masses of all naturally occurring isotopes of each element in a molecule.
Key Areas Covered
1. What is Monoisotopic Mass
– Definition, Features
2. What is Average Mass
– Definition, Features
3. Similarities Between Monoisotopic Mass and Average Mass
– Outline of Common Features
4. Difference Between Monoisotopic Mass and Average Mass
– Comparison of Key Differences
5. FAQ: Monoisotopic Mass and Average Mass
– Answers to Frequently Asked Questions
Key Terms
Monoisotopic Mass, Average Mass
What is Monoisotopic Mass
Monoisotopic mass refers to the mass of a molecule. It is calculated considering the mass of the most abundant isotope of each element present in the molecule. Isotopes of an element are the variants that have different number of neutrons in the nucleus hence have different atomic masses. For example, chlorine has two stable isotopes: chlorine-35 and chlorine-37. The average atomic mass of chlorine is approximately 35.45 amu but the monoisotopic mass is only considered as -35.
Figure 1: Orbitrap Mass Analyzers
The accurate masses of the most abundant isotopes of all constituent elements are added together to determine the monoisotopic mass. This is mostly useful in mass spectrometry, which is a method that measures the mass to charge ratios of ions to identify the compounds. Here, monoisotopic mass is used in compound identification, isotope pattern analysis, and quantitative analysis. It is also useful in drug discovery, proteomics, metabolomics, and in forensic science.
What is Average Mass
Average mass is sometimes called atomic weight. It represents the typical mass of an atom of an element as present in nature. Every atom of an element is not identical. In certain elements, there are isotopes with different masses. For example, chlorine-35 is more abundant, so it contributes more to the overall average mass of chlorine, which is approximately 35.45 amu (atomic mass units).
Average mass is used in stoichiometric calculations, mole conversions, determining empirical and molecular formulae, and balancing equations. It is also used in chemical reactions, in mass conservation and yield calculations. Furthermore, in analytical chemistry this concept is useful in concentration calculations and quantitative analysis. In addition, material scientists use it in composition analysis.
Similarities Between Monoisotopic Mass and Average Mass
- They are numerical values representing the mass of a chemical entity.
- Both are based on the masses of isotopes.
- Both are used in chemistry and related fields.
Difference Between Monoisotopic Mass and Average Mass
Definition
- Monoisotopic mass is calculated using the masses of the most abundant isotope of each element in a molecule, while average mass is calculated as a weighted average of the masses of all naturally occurring isotopes of each element in a molecule, considering their relative abundances.
Precision
- Monoisotopic mass is more precise than average mass.
Use
- Monoisotopic mass is a theoretical value based on the assumption of the most abundant isotopes, while average mass is a practical value representing the typical mass of an element as found in nature.
Conclusion
Monoisotopic mass and the average mass are two mass measurements widely used in chemistry. The monoisotopic mass of a molecule is calculated using the mass of the most abundant isotope of each element present, whereas average mass is the weighted average of the masses of all naturally occurring isotopes of each element in a molecule.
FAQ: Monoisotopic Mass and Average Mass
1. What is the average mass in mass spectrometry?
Average mass in mass spectrometry is the weighted average of all isotopes present in a molecule. It considers the abundance of each isotope to calculate the overall mass.
2. What is the difference between average mass and atomic mass?
Average mass is the mean mass of multiple objects. Atomic mass is the weighted average mass of an element’s atoms, considering different isotopes and their abundances.
3. How to determine monoisotopic mass?
Monoisotopic mass is the calculated mass of a molecule using the most abundant isotope of each element. You can calculate it by summing the exact masses of these isotopes.
4. What is the difference between average and relative mass?
Average mass is the mean mass of multiple objects, while relative mass compares the mass of one object to another, often using a standard unit.
Reference:
1. “Monoisotopic Mass.” Science Direct.
Image Courtesy:
1. “Orbitrap Mass Analyzers” By Thermo Fisher Scientific (Bremen) (CC BY-SA 3.0) via Commons Wikimedia
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